The linear motor comprises a field magnetic pole and an armature facing the field magnetic pole, one of them being employed as a stator, and the other as a needle. A moving coil linear motor has the field magnetic pole as stator and the armature as needle, and a moving magnet linear motor has the field magnetic pole as needle and the armature as stator.
In patent document 1 (JP-A-2000-278931), a moving coil linear motor was disclosed in which to suppress a cogging thrust produced in the linear motor, the armature is divided into a plurality of blocks, with a phase difference provided between divided blocks of the armature, whereby the produced cogging thrust is offset between armature blocks.
In the patent document 1, to provide the linear motor with the suppressed cogging thrust, shorter length of armature in the thrust direction and higher coil temperature detecting precision, the armature is divided into a plurality of armature blocks that are arranged in the thrust direction, in which a block core of each armature block has the teeth arranged at an equal pitch, the number of teeth being an integral multiple of the number of phases, the teeth being provided with an armature coil with concentrated winding, and the armature coil of each armature block is shifted in phase by an electrical angle corresponding to an interval between armature blocks to provide a phase difference in the cogging torque caused in each armature block, the cogging torque being offset to null the sum of cogging torque.
The linear motor as described in patent document 1 is constituted to suppress the produced cogging torque, with a structure in which all the teeth of the armature has the winding, the windings of different phases being adjacent within each slot, and to enhance the insulation of the motor, there is a need for providing the measures for reinforcing the insulating material such as a coil film or interlayer paper or decreasing the amount of coil within the slot to keep a distance between the coils within the slot, as described above. A method for enhancing the insulation of the motor by reinforcing the insulating material such as coil film or interlayer paper had a problem that, because the insulating material such as coil film or interlayer paper is varied in the degree of deterioration due to constituents of the cutting water, the insulating material is difficult to select, and the material cost and the number of manufacturing steps are increased.
Also, another method for enhancing the insulation of the motor by decreasing the amount of coil within the slot to keep a distance between the coils within the slot had a problem that the motor performance is sacrificed, because the motor has more field ohmic loss due to the decreased amount of coil.
Also, another method for enhancing the insulation of the motor had a problem that the whole motor may be covered with resin to prevent intrusion of the substance that deteriorates the insulation, but when the resin is damaged by biting chips, the cutting water possibly intrudes through a damaged portion to deteriorate the insulation.
This invention has been achieved to solve the above-mentioned problems, and it is an object of the invention to provide a linear motor in which the produced cogging thrust is suppressed, and the insulation of the motor is enhanced simply.